Game version: 50.07

I embarked right next door to necromancer tower of Copperblazed (ruled by The Blockaded Priests before my dwarves conquered the place)

Multiple years after the founding of my fort, I conquered them and established a new ruling organization (The Sabres of Righteousness, oddly enough it doesnt have administrator)
I called my dwarves back (2 human mercenaries just vanished there, seemingly being occupiers)

The tower had no histfigs before I sent there my dwarves (3 werecavy units were moved there for safety of my fort)

The population on conquest was around 20

But then it gradually grew

After it hovered around 50 units in the tower, it sent a siege to me despite it being my holding

Siege was defeated by female macedwarf who died of old age and got revived very close to necromancer, but one enemy necromancer remains in the far left part of the map who is just listed as "Hostile" (he didn't retreat after siege defeat for some reason)

Interestingly enough, the tower shows "Peace"